It must stay decentralized and secure, and its use as a MoE is part of that, due to the nature of the protocol: if people don't use it, the tx fees will not fund much security, which will undermine its value proposition as a SoV.

But if we put the tech aspects aside, assuming security, and only consider the monetary properties, I don't think an asset needs to be a widely adopted MoE to be a good SoV. Just the fixed supply and the ability to spend it permissionlessly are sufficient to make it a good SoV, because they're an improvement over other SoVs, and will siphon monetary premia from other assets.

For it to store value it doesn't need to be the money you use to pay for coffee, if you can sell it for something else (e.g. fiat clown tokens) and use that to pay for your coffee. If fiat on- and off-ramping becomes too much of a choke point, merchants can start accepting it directly. As long as people can sell it or spend it, it can be used as a SoV.

An example to prove that would be gold. You can't pay for coffee by shaving off a piece of a gold bar, but it is a SoV, because you can sell it.

Another example would be foreign currencies. The Norwegian krone is not widely adopted on this planet. No restaurant in NYC will accept it. But you can exchange it for dollars and therefore it has value.